Gaseous discharge system



c. J. R. H. voN WEDEL. 2,084,750

June 22, 1937.

GAsEoUs DISCHARGE SYSTEM Filed Jan. 29, 1935 am. mm,

A TTORNE y Patented .Func 22, 1937l GASEOUS DISCHARGE SYSTEM Carl J. R. H..von Wedel, West Orange, N. J., assignor to Thomas A. Edison, Incorporated, West Orange, N.'J., a corporation of New Jersey Application January 29, 1935, Serial No. 3,891

24 Claims.

The present invention relates to gaseous discharge systems, and especially to systems operatingirom alternating current to provide a luminous aredischarge It will be understood, however, that various sub-combinational features of the invention may be useful in other than such particular dischargesystems. l

.Y An .important object of the invention is to pro vide a system of the type described which opermates with a very high. eiciency. of light output from theluminous column relative to power in- An allied object is the reduction ofthe ballastingmeans normally required in such a.v system.

the flicker` oiA the luminousfcolumn. ordinarily occurring 'in such systems.

Still another object is the extension of the range of supply voltage over which the system 20 will `satisfactorily operate.:l

Yet another object is: the improvement of the color ofthe light emitted by the luminous column.

Amore detailed object of my invention is the provision o f -a small cathode requiring a mini- 25 mum of heating power and characterized by an improvedlife. v

Another such object is the provision of animprovedrectiiier structure wherein the anodes and cathode are relatively closely spaced.

Sti-ll anotherrsuch object is the provision of improved and more dependable means for start- .ing the arc discharge.

Other and allied objects will more fully appear from the following' description and the appended claims. v

In the description reference is had to the accompanying drawing, of which:

Figure i is a view of a discharge device and an associated circuit according to my invention, the

40 discharge device appearing principally in section and the circuit schematically;v

Figure 2 is a cross-'sectional view taken along the line 2-2 of Figure 1, illustrating the interior of one of the electrode structures;

portion of the electrode structure';

Figures 4. 5, and 6 are cross-sectional ,views taken along the lines 4 4, 5-5, and 6-'B of Figure 1; and l,

Figure 7 is a schematic vievr of aspecial form of transformer which 'may advantageously be employed in the circuit'of AFigure 1.

Reference is first invited to Figure 1. Herein appears an elongated glassV vessel or other en- 55 velope l, adapted to contain a gaseous filling- 'Another important object isrgthe reduction of v Figure 3 is an enlarged elevational view of a i. e., a iilling of gas and/or vapor-in which to.

electrode structures 2 and 3 are suitably posi.

tioned Within the envelope, forexample at its respectively opposite extremities, the arc discharge being intended to take place between these structures.

The electrode structure 2 comprises the main cathode 4 of the device together with a shield can 'therefor, while the structure 3 comprises the two anodes t and l0, a second or auxiliary cathode t whose function is hereinafter more parf ticularly set forth,'and a shield can l about the cathode 5. Both the cathodes 4 and 5 'comprise thermionic elements-i. e.,"elements favorably' adapted to emit .electrons when heatedand have been illustratedA as coiled filaments.'v These have been shown arranged to be at leastpartially heated by currents fromtheheating windings i4 and l5 of thetransformei'* I3, but it will.

be understood that many of 'the' featuresof my invention are adaptedfor employment as well with other forms of cathodes, such as normally cold cathodes adapted to be heated substantially wholly by ionic bombardment attendant upon the main arc discharge, or indirectly heated cath- A odes of well known structure wherein activated metal surfaces are heated by adjacent heating coils.

The electrode structure 3 may conveniently be first described, reference being had to the crosssectionai Figures 2, 4, and 5 and to the enlarged fragmentary Figure 3, as well as to Figure 1. The 1 cathode element 5 is preferably made from a heater wire 5' onto which has been wound -and welded a ne wire 5". The wire 5 is coiled into the form oi a helix, the turns of which are re1- atively close to one another, excepting that they are divided into itwo groups .by a spacing, at

about the longitudinal center of the helix, of the order of 2 to 2% times the side dimension of apertures 1e hereinafter referred to. The cathode 5 is coated with a rather heavy Wehnelt type oxide coating.

The cathode 5 is supported within and shielded by a cylindrical can or thimble 1, which is made of an internal diameter only slightly exceeding the external diameter o! the cathode 5. The can 1 is provided with anodeshielding venes 8. and

may conveniently be formed, as appears in Figure 4, of two similar metal plates 1', each in the form of a semi-cylinder from which extends in an axial plane one of the vanes 8, the plates being appropriately assembled and welded together. Each vane B may be provided with a right-angular flange 8' at its outer extremity. The ends of the cylinder may be closed by the cup-shaped metallic top and bottom members 1a and 1b respectively. A i'lrst extremity 5a of the cathode 5 may be led through the top member 1a and welded to the outside of the top member (thereby rendering the shield can 1 at the potential of one extremity of the cathode), while the other cathode extremity b may be led outwardly of the can 1 through an isolantite or other insulating bushing 1c inserted centrally in the bottom member 1b, and outwardly of the envelope I through the stem or seal I' to be electrically connected to one extremity of the heating winding I5 of the supply transformer I3. The can 1 is supported to the seal I' by small rods 1d welded to the can, one of these rods extending through the seal to f' be electrically connected to the other extremity of the heating winding I5. -The cathode is arranged to operate at a relatively low voltage- 'vided with two apertures 1e.

of the order of 2 to 3 voltsand the coated fine spiral wire 5 on the wire 5 insures sumcient insulation from the can 1 should the cathode sag or Warp into contact With the can. It also prevents shorting between adjacent turns of the helix.

The anodes 9 and IIJ are disposed on .opposite sides of the shield can 1, preferably very'4 closely spaced from the vanes 8 and generally within the Ls formed by the vanes B and their anges 8'. The ano'des are supported on the rods 9 and I0', vthese passingV outwardly through the envelope seal I'. 'I'his seal is shown provided with the beads or extensions 9." and I0", these extensions surrounding the respective rods 9 and I0 to within the respective anodes. and Ill' are electrically connected to the respective extremities Id and Ile of the high voltage winding I6 of the transformer I3. This high voltage winding may be tapped at points Ilia and IIb, symmetrically located about its centerpoint, to form a primary for connection to .the alternating current supply. 0n this transform-1 er I3 are also wound the separate heating windings I4 and I5 elsewhere mentioned.

The cylindrical portion of the can 1 is pro- These may be square, and of a. size hereinafter more fully specied. Longitudinally of the cylinder, these apertures are approximately centralized with the central spacing of the helix above mentioned; in the other dimension they are approximately centralized in a plane passing through the'cylinder axis normal to the plane containing the axes of the two anodes-in other words they are situated on opposite sides of the cylinder in each case approximately midway between the anodes.

'I'he electrode structure 2, comprising the main cathode 4 of the device and a shield can 6 therefor, may be formed of components quite similar and similarly arranged to the components of the electrode structure 3, excepting thatlthe vanes 8 and the anodes 9 and I0 with their supporting means are omitted from the structure 2. The components of the structure 2 are supported to the seal I", located at the opposite extremity of the device from the sealfI', and ineach case are designated in the figures by numerals less by l than those provided for the respectively of the electrons which in the operation of the cathode leave the cathode surface and travel perpendicularly toward theaxis of the helix. The reason for this specification is that the electronic current leaving the cathode surface and proceeding toward the helix axis must be able to build up a region of positive space charge about the axis, otherwise the discharge will take place only to the portions of the cathode immediately adjacentthe shield can apertures. This positive.- space charge can of course not be created at a region nearer to the cathode than the mean free path of the electrons. This mean free path is o1' course dependent on the density and molecular weight of the gaseous filling which exists within the shield .can under operating conditions; In a discharge device' operating with a gaseous illing comprising both rare gas and metal vapor,

the gaseous filling within both the shield can and the rest of the device when the discharge is rst started is of course of substantially pure gas. As the temperature of the device rises, however, increasing densities of metal vapor are formed in the device. 'I'he vapor molecules, being preferredly ionized, then enter the shield can, and by virtue of their greater mass largely displace from out of the can the gas molecules; thus when the device has reached full operating temperature the gaseous filling within the shield can is largely of metal vapor. The mean free pathv of the electrons will vary with these varying conditions of the gaseous filling in the shield can, and it is desirable that the longest mean free path attained by the electrons under any of these conditions be appreciably exceeded by the radius of the cathode. At.` the Same time this radius is jpreferably not permitted to attain an unnecessarily large value. As a specic example, a cathode internal radius of 2 to 21/2 millimeters has been'. found satisfactory in a discharge device having a gaseous filling of krypton or argon at a pressure of 2 to 2.1/2 mm. Hg together (when the device has reached full operating temperature) with mercury vapor at a pressure corresponding to a wall temperature of 60 to 90 degrees C., the cathode'then operating at a temperature of 800 to 900 degrees C.

The length of the cathode should not be too great relative to the cathode diameter; a ratio of length to diameter of the order of v2 or 21/2 to 1 is however permissible. The reason for this specication is that if the cathode is excessively long relative to its diameter there will develop along the cathode axis a signicant potential gradient, which will c ause the discharge to take place quite predominately to the portions of the cathode immediately adjacent the shield apertures. In the y case of the typical device above mentioned, a satisfactory cathode length was of the order of 10 millimeters.

The most desirable size of the apertures in the shield can .varies with the value of the discharge currentwhich is .to take place to the cathode. 'Ihe apertures must be made small enough to prodlle an appreciable potential gradient in the disrents ofthe order of 2 amperes, which is the approximate discharge current in the luminous column ,of the typical device above mentioned, the

. apertures may satisfactorily be approximately tion of the glass walls of the envelope l.

2 by 2 millimeters.

The structure of the cathodes having thus been described,'fsome of the advantages of this structure lgeneric t the ltvvoV cathodes may be set( forth. In the first place a cathode of this form may be heated most eiiici'ently---el g., a very low value of heating current may be employed-because the shield can tremendously reduces the gaseous convection currents between the immediate neighborhood of the cathode and otherV and coolerportions of'the discharge device. Thus a cathode of this form to support a 2 ampere discharge may be satisfactorily heated by only l5 watts and may be correspondingly small, as compared with a larger cathode operating with 30 or 40 watts required to perform the same function when exposed to the mentioned gaseous convection currents. For the same reasona short length of time for the initial heating of the cathode is i assured. Again, the high current density in the shield can apertures enforces ionization of alkaline earth material disintegrating from the cathode surface, so that the eld of the tube transports this material back to the cathode, improving the cathode life and avoiding discolora- Further, in the particular case of devices operatingwith a filling including metal vapor, the extra high vapor density within the shield can relative to other space Within the device, above explained, reduces the vaporization of cathode material, providing a longer -cathode life and/or permitting a smaller cathode for given discharge current thereto. Finally, and independently of the nature of the gaseous filling, the discharge, entering the shieldA can through its two apertures, is thereby forced to enter into the axial space within the helix, and therefrom diffuses in a most even mannerover the entire inner cathode surface, eliminating the danger of uneven or spot-.heating of the cathode.

In devices operating Vwith a filling of rare gas andmetal vapor, the use of the described cath'- ode structure for the main cathode of the device has an additional advantage.V In the operation immediately following the starting of such devicesjthe potential gradient of the luminous column increases with the steadily increasing metal vapor density until the device reaches its nor'- mal operating temperature. In such tubes with the described form of cathode structure, however, there is a tendency for the potential gradient in the shield can apertures to beinitially higher than after .the device has reached normal operating temperature, this offsetting to some extent the change of potential gradient of the luminous column, reducing the net potential change across the entire device and permitting the reduction of the usual series ballasting means and of the power consumed therein. This action may be assisted to some extent, or produced to some extent in devices having this cathode structure but operatingwithout metal vapor in the filling, by an initially extra high cathode drop brought about by employing for the cathode a heating current somewhat less than required for full emissivity of the cathode. This I have found it permissible to do because this cathode structure has proven well adapted for some additional heating by ionic currents, without danger of puncturing by spotheating of the cathode surface v Certain advantages exist particularly with relation to the electrode structure 3 as above described. In the first place, the vanes 8 provide goed shielding of the anode sur-faces, preventing cross-arcing therebetween and undue ionic bombardment thereof. Further, by virtue of the -relatlve disposition of the anodes and the apertures le, disintegrating anode material is substantially prevented from iiying to and contaminating the cathode surface; with carbon anodes this minimizes the deposit of carbon on the cathode and the attendant formation of undesired gases in the discharge path. Again, such disintegrating cathode material as may not be ionized in the aperturesv 'leand transported back to the cathode is flung from the apertures toward the envelope walls, preventing contamination of the `l anodes thereby.

ode alternating current discharge devices it is f customary to connect the center-tap of the high voltage supply to the cathode of the device through a choke coil anda series ballasting resistance or lamp. The choke coil both limits the peak discharge currents and also slightly prolongs each successive discharge so that it extends to an instant at which the succeeding discharge (to the,

other anode) can begin'. Viewing the choke coil action in another light, it reduces the pulsations in the voltage between cathode and the instantaneously most 'positive anodic element (i. e., the

vvoltage across the luminous column), both limiting the peaks and raising the valleys in this voltage. A strong pulsatlon or ripple component having a fundamental or main frequency of .twice the supply frequency still remains in this voltage, however, and in the current through the choke coil and is responsible for the flicker of the light produced by the luminous column.

An importa-nt feature of my invention is the reduction of this ripple component, whereby the light icker is reduced. This reduction I accomplish by inducing into the choke coil a ripple voltage appropriate to oppose the ripple voltage between the cathode and the instantaneously most positive anodic element. The ripple voltageV induced may be otherwise defined as one approprlate to cause the potential of the cathode extremityof the luminous column to fluctuate similarly in phase, amplitude and waveform to the potential of the anode extremity of the column appropriate to oppose current fluctuations in the choke coil;this definition is synonymous with the others, since the current through the choke coil is the same as the current through the lumi- Winding Mrfor this cathode).

nous column, and if voltage fluctuations across the luminous column are opposed the current fluctuations are opposed, and vice versa.

A circuit appropriate for addition to the conventional system to effect the required ripple induction might theoretically be formed of an auxiliary coil, tightly coupled to the choke coil in proper polarity and an appropriate condenser in series With the auxiliary coil, this series circuit being connected between the input extremity of the choke coil and the instantaneously more positive anode. Practically, of course, it is impossible to make a direct connection to the instantaneously more positive anode, since this would require a connection which automatically shifted cyclicly from one anode to the other and back again. I have found, however, that such a series circuit may advantageously be connected between the input extremity of the choke coil and an emissive cathode located closely adjacent the two anodes. Such a cathode forms with the two anodes an auxiliary discharge device or rectifier in which, by virtue of the close spacing of its elements, the voltage drop when the device i's discharging is extremely low.

Reference may be conveniently had at this point to Figure 1, which may be considered for the present with the choke coil 5 8 omitted (i. e., short-circuited). The center-tap IB'- of the high voltage winding I6 is then connected to the tap 28 on the choke coil 28. This tap divides the total coil into two sections: one 28a, which is preferably the larger Aof the two and which forms the choke coil as discussed in the preceding paragraphs; and the other 28h, which is preferably the smaller, which forms the auxiliary coil discussed above, and which is of course tightly coupled to the section 28a. The tap 28' forms the inpu extremity of the section 28a, the `other or output extremity of which is connected, through the'series ballasting resistance or tungsten lamp 22 to the main cathode 4 (the connection tothe cathode being made if desired through the medium of a center-tap I4 on the heating The outer extremity of the section 23h is connected through the condenser 33, which comprises the condenser discussed in the preceding paragraph, to the rectifier cathode 5 (the connection to this cathode being made if desired through the medium of a centertap I5 onthe heating winding l5 for this cathode). The preferred physical formation of the cathode 5 and its disposition relative to the anodes 9 and I0 have already been outlined.

For the ripple inducing circuit to function properly, there must be at least very approximately established a. proper inter-relationship between its parameters-i. e., between the constants of the choke coil 28 and the capacity'of the condenser 33. It seems that theoretically the c apacity of the condenser 33 should be of the order of magnitude of the-.capacity required for resonance.' to the. ripple frequency, with the mutualA inductance between the auxiliary choke section 28b and the entire choke coil. (This mutual inductance is the samefas the sum of the self-inductance of the auxiliary section 28h andtheA mutual inductance between the two sections 28a. and 28h.) 'Ihis capacity value I have not found sharply critical, however, and I have satisfactorily employed '-for 33 arcondenser of a fraction ofthe value indicated above. More broadly, then, the capacity value maybe specified as. one of the order required, for resonance to the ripple frequency with the total inductance of the choke coil 28-i. e., of the sections 28a and 28D mutually aidingly coupled.

The explanation of beneficial result from the connection of the ripple inducing circuit33-28b to the rectifier cathode 5 appears to be that the potential of this cathode in-a very general sense approximates that of the most positive anodic element. This is because if its potential rises above that of the instantaneously more positive anode, the rectifier cathode (and its shield l) will itself become the most positive anodic element (under which conditions it will support at least a portion of the main arc discharge, thus lowering the charge in condenser 33 and reducing the rectifier cathode potential); while whenever the rectifier cathode potential is several volts lower than the instantaneously more positive anode potential, current is passed in the rectifier. charging the condenser 33 and raising the rectifier cathode potential.

Therectier supports' a ripple current flow through the circuit 33-2827, by virtue of which flow the circuit performs its function of ripple voltage induction into the choke section 28a. This ripple current flow, however, is strongly displaced in phase from the instantaneously more positive anode potential; it appears that it tends to lead the latter by very roundly 90 degrees in a ripple cycle. itself capacitive, and would cause the ripple current iiowing through it to be advanced by something less than 90 degrees; its coupling to the when ' choke section 28h and the ripple current through the latter, however, are responsible for the additional phase displacement) Apparently this displaced phase condition of the ripple` current through the circuit 33-28b causes the approximation of the potential of the instantaneously most positive anodic element by the rectifier .cathode potential to be only fair-a condition which reacts on the ripple current in question to affect its characteristics unfavorably to its function of proper ripple voltage induction. However, with this circuit arrangement (i. e., without the choke coil 58) I have been able approximately to halve the ripple current through the choke section 28a, and hence markedly to reduce the ripple voltage across the luminous column and the light flicker; this is by comparison toa simple circuit in which theA choke coil employed was identical with the entire choke `coil 28 of the' described circuit.

I have found that if, in the circuit as described, I insert the additional choke coil 58 between the center-tap of the high voltage winding I6 and the tap 28 on the choke coil 28, I reduce to substantially zero the ripple current through the choke section 28a, the ripple voltage across the luminous column, and the light icker. The inductance ofthe choke coil 58 must be materially greater than that value which, when added to the inductance value of the auxiliary choke section 28h, will resonate with condenser 33 to the ripple frequency. This is flrstnecessary to avoid dangerously: high ripple voltages across the condenser 33 which might cause its break-down, and

secondly is desirable for the function of icker elimination. Thus the value of the choke coil 58 may be of the order of that of the choke section 28a, and may even be larger.

Apparently an important function of this choke coil 58 is a substantial retardation ofthe ripple current through the circuit 33-28b, bringing this current more closely into phase with the instantaneously more positive anode potential aosaveo and improving the approximation by the rectiiier cathode potential of the potential of the instantaneously most positive anodic element. The choke coil 58 of course renders inductive the simple circuit 3a-23h; because of the coupling of this circuit to the choke section 28a, however,.the current retardation may not be wholly suicient to render the ripple current through the circuit in phase with the instantaneously more positive anode potential unless the choke coil 58 be made of very high inductance. In any event it appears that a choke coil of the order mentioned is suiiicient to provide ample retardation of the ripple current. Another function which it is possible for the choke coil 58 to perform, in cooperation with the succeeding circuit elements 28 and 33, is the actual filtration of the ripple current nowing between the high voltage winding l and the main cathode d. This function is only signincantly performed as to the main ripple frequency with relatively high inductance values for the choke coil 53, which I have found it unnecessary to employ; as to ripple components at harmonics of the main ripple frequency, however, this function is probably always more or less significantly performed. The 'choke coil 58 of course exerts a `retarding influence not only on the ripple current through the circuit SS-Zln but also on other ripple currents in the system; because of similarity of these retarding influences, however, the relationships between the parameters of thechoke coil 23 and the condenser 33 as above outlined remain satisfactory when the choke coil 5B is inserted in the circuit. l

With the circuit constructed and properly apportioned as thus 'described the voltage across the luminous column is substantially free of iiuctuation and the discharge current is substantially pure direct current. The absence of appreciaable peaks facilitates the use of a small ,cathode d, it being well known that the capacity of the cathode must be in conformity with the peak' maximum discharge current thereto. The cathode 5, passing only the current required for the ripple inducing circuit S3-28h, operates under less current stress than the cathode l, and therefore need obviously be no larger.

The system must not be confused with one wherein the current for a D. C. discharge device is rectied 'and smoothed by a rectifier and iilter external to the device. Not only is its structure and mode of operation obviously distinct therefrom, but it has important operational advantages thereover. In the separate rectifier system the rectiiier would be called on to pass the entire discharge current for the device. Consequently,

such an external rectier having to pass much more current than the rectifier in my improved system, the power losses would be materially higher, the cathode of the external rectier would have to be much larger than my cathode 5 or even my cathode d, since it would have to withstand not only the full device discharge current but also large peaks therein;"a second anode fall would have to be accountedv for, which is absent in my system in View of the employment of only one pair of anodes; etc. Even though I employed for. my rectifier a full-wave rectifier external to the' discharge device with anodes respectively connected with the device anodes, which I might less preferredly do, practically all 'of these distinctions would still obtain.

The important advantages of the circuit arrangement which I have described do not stop with the substantial elimination of discharge current ripple and of light flicker. Another most important advantage, assuming the device to be employed with a given value of ballasting means (e. g., lamp 22) is a tremendous increase in the range of supply voltage over which the device will operate without extinguishment of the discharge or otherundesirable effect. The principal reason for this may be simply outlined as follows:

In the operation of a discharge device the instantaneous discharge current in each cycle will iiuctuate over a range which is very roughly proportional to the fluctuation of voltage in each cycle across the luminous column. A'Ihere is, as

is well known, a lower limit of discharge current.

through a given discharge device below which the minimum instantaneous current cannot be permitted to fall without discharge extinguishment. Likewise lthere is an upper limit above which the instantaneous current should not be permitted to rise, this upper limit being very critical as to discharge extinguishment in the case of tubes operating with a filling including metal vapor. When the voltage iiuctuation across the luminous column is appreciable the minimum and maximum current values may approach respectively the lower and upper current limits just mentioned. If now the mean supply voltage varies appreciably, either the minimum or maximum instantaneous current value (as the case may be) may pass its respective limit. Indeed, the way in which a reasonable tolerance to varying supply voltage is normally obtained is by the use of a very substantial value of ballasting means, which of course has a stalbilizing efect on the current. In my improved circuit arrangement the voltage fluctuation across the luminous column is substantially zero, the minimum and maximum instantaneous current values are therefore practically coincident, and therefore the minimum current value is much larger and the maximum current value much smaller than the corresponding values with conventional circuits. Accord- 'ingly the' supply voltage must vary very much.

more widely before either current value may pass its respective limit.

The'vast increase therein renders the permissible range of supply voltage variation quite unnecessarily large, and accordingly I am able greatly to reduce the value of the ballasting means. This in turn enables me to make any one of several advantageous readjustments of the parameters of the circuit and/or device proper, while retaining a satisfactory permissible supply voltage range. Three particular such readjustments may be mentioned, any one of which may be eiectedvto a large extent alone, or to a reduced extent in combination with one or both of the others. First, I may reduce the size of the high voltage Winding i6 appropriately to the reduction of the ballasting means, thereby reducing the power consumed by the system; the light output remaining constant, however, the efficiency of the system is improved. Secondly, I may increase the length of the luminous column appropriately to the reduction of ballast, increasing the iight output oi the system without increasing its power consumption. Thirdly, I ma'y operate the discharge device with a higher discharge current; this, at least in the case of a device operating with a filling including metal vapor, improves the color of the light emitted by the luminous column. For example, with a device employing mercury as a vaporizable metal and having envelope Walls of a yellow uranium glass, the color of the emitted light becomes more Whitish-green in character and more pleasing to the eye. It may-be mentioned that the character -of the light can be further improved, when operated with this greater current density, by lncluding in small quantities with the-mercury, as further metal adapted for vaporization, alkaline metals and metals such as cadmium, zinc, thallium and other metals whose vapors are of lower ionization potential than mercury vapor.

Thatportion of the circuit directed to the maintenance of the discharge having thus been described, attention may be directed to the further circuit components which, in cooperation with those already described, serve to start the discharge. These components are comprised in a. starting" circuit connected between the two cathodes 4 and 5 (for example through the media of the center-taps I4' and I5 of the respective heating windings for these cathodes) Connected to the cathode 4 is the interrupter 29l and thereto the coil 30a,in parallel with which two elements is a condenser 38. 'Ihe coil 30a with the condenser 38 may form a circuit resonant to a. high frequency. The interrupter 29 is closed when the system is inoperative, and carries an armature 29a positioned for attraction by the core of the choke coil 28, so that when thechoke section 28h becomes loaded with suiiicient direct current the interrupter will open. From the coil 39athe starting circuit passes through the thermostat 3i, which comprises a heatable resistance 3Ia and a switch 3|b which is open except when the resistance 3Ia is hot. From the thermostat 3| the starting circuit passes through the current limiting resistance 32 to the cathode 5. The starting operation may be outlined as follows:-

As soon as the terminals 18a and |6b are connected to the alternating current supply source, the cathodes 4 and 5 are provided with heating current and the anodes- 9 and I0 with high alternating potentials. By virtue of the voltage of the high voltage winding I6, the full-wave rectifier formed by the anodes and the cathode 5 starts immediately with a glow discharge to pass a current. This current charges the condenser 33 to the peak voltage of half the high voltage Winding I6. The current also ows through the starting circuit, the choke section 28a, and the choke 58. The resistance 3| a of the thermostat (together with the resistance 32') limits the current to a very small value until it has become hot, whereupon it is shorted out by the closing of switch 3Ib. The heating period of the thermostat is arranged to give the cathodes .an opportunity to become fairly well heated by their heating currents; this period may be made relatively low, however, because of the relatively rapid heating of the cathodes. When the thermostat resistance is shorted out a sudden increase of course occurs in thel current through the rectifier, the starting circuit, the choke section 28a and the choke coil 58. The heavier current is now sui"- cient so that its flow through the choke section 28a causes the attraction by the choke core of the armature 29a, opening the interrupter 29 and abruptly breaking the flow of this heavier current through the choke section 28a and the coil 30a. The breaking of the currentfiow through the choke section causes the production thereacross of a high voltage kick, and thebreaking of the current flow through thecoil 30a causes the superimposition on this kick of a high frequency oscillation. By virtue of the circuit position of the choke section 28a this kick (together with the its shield can 1) on the one hand, and the cathode` 4 on the other hand. This causes ionization of the gas path and starting of the arc discharge; the flow of the discharge current through the choke section 28a then maintains open the interrupter 29 and hence the starting circuit, and the thermostat resistance 3la cools down and sets the thermostat for another operation.

While I prefer to utilize the high frequency oscillation ln'addition to the kick across the choke section 28a, it is in many cases dispensable and the circuit may then be operated without the high frequency oscillation; in this event the coil 30a would be omitted (i. e., short-circuited) and the condenser 38 would be omitted (i. e., open-circuited). When the high frequency oscillation is employed, and with discharge devices in the form of tubes of over about 60" in length, it may be desirable to aid the high frequency ionization of the discharge path by surrounding the tube at an intermediate point by an external electrode 52, this being connected to an extremity of the secondary 30h of a high frequency transformer or Tesla coil 30 of which the coil 30a forms the primary.

Starting circuits have heretofore been connected from the main cathode of a discharge device to one of its anodes, or to some point in the high voltage winding supplying the anodes. Such circuit'arrangements are not to be confused with my improved arrangement. In the latter the rectifier formed by the anodes and the cathode 5, in association with the condenser 33, provides a source of substantially pure direct current for the starting circuit, insuring against the opening of the interrupter 29 at an instant of 'low current flow with resulting feeble kick. Still more signicantly the rectifier and the condenser 33 cooperate to provide, up to and including the instant of the kick no matter when in a supply cycle the kick may occur, an anodic element at the maximum available positive potential relative to the main cathode 4-i. e., at the potential of the peak voltage of half the high voltage winding I6. This anodic element is the cathode 5 together with its shield can 1; and the effect of its certain high Y' positive potential relative to the main cathode element is at a high positive potential relative to the cathode. Thus I provide improved and more dependable starting of thedischarge.; furthermore I do this principally by means of components-i. e., the rectifier and the condenser 33-which already are adapted to perform other highly important circuit functions as set forth in detail hereinabove. It may be noted that the condenser 33 is so positioned in the circuit that it is not affected by either the starting kick or the high frequency oscillation, so that its function in the starting operation does not increase the requirementsv for dielectric strength in the condenser.

The transformer I3 has been illustrated in a wholly schematic manner in Figure 1. While it may be of entirely simple and conventional design, I have found it advantageous, particularly in connection with discharge devices operating with a filling including metal vapor, to make the transformer structurally of a constant current 45 vention.

portionment of the core, as is well understood,

the stray iield lines between the core legs 53h and 53d may be made significantly to increase l with the current loading of the core, and consequently the voltages induced in the windings on the core leg 53e reduce as the current demands thereon increase.

This arrangement as to the heating windings is always advantageous because the initial heating currents (when no main arc discharge is taking place and hence no heavy current is being drawn from the Winding i6) may be made relatively high for quick cathode heating; as soon as the main arc discharge starts and becomes available to aid in the cathode heating by recombination of ions on the cathode surface, the heating currents from the transformer are automatically reduced. The arrangement is also advantageous as .to the high voltage winding iii, particularly with devices operating with a filling including metal vapor, since it largely counteracts the tendency for excess current to flow in the early portion of the main arc discharge (as a result of the then lower potential gradient of the luminous 4column discussed hereinabove). In this connectionit will be apparent that a transformer of this type will further facilitate the reduction of the value of the ballasting means (e. g., lamp 22), which has already been shown to be capable of great reduction in connection. with other features of my invention.

I have above recited certain typical parameters of a discharge device proper according to my in- I may here augment those recitations by setting forth certain further typical parameters of a system incorporating such a device. These are derived from observations made upon a particular system actually constructed and satisfactorily operated, but in 'which the choke coil 58 was not employed; accordingly appreciable discharge current iiuctuation remained and compelledthe use of a higher value of ballast means (with correspondingly greater high voltage winding i6 and/or less luminous column length) than necessary in the preferred embodiment of my invention wherein the choke coil 58 is employed.

In this system the discharge device was filled 60 with krypton gas at 2 to 3 mm. Hg pressure, and was provided with a supply (e. g., globule 2l) of mercury adapted for vaporization. The cathcde's d and 5 were similar and consumed (in the absence of discharge) approximately '7 amperes of current at 2.5 volts.

each half of the high voltage winding i6 was approximately 110 volts. The main arc discharge current was measured at 2.2 amperes D. C., representing a current density of about 1 ampere per square centimeter of cross-section in the positive column. The column length was 108 centi` meters (measured from cathode shield 6 to cathode shield l) and the D. C. voltage drop in the column was measured at 60 to 65 volts. The D. C. voltage drop across the tungsten ballast The voltage of lamp 22 measured 2U volts. The inductance of the choke coil section 28a under load was of the order of 1/15th henry; the choke coil Section 28h had approximately 1/3 as many turns as had the section 28a. Accordingly the sum of the self inductance of the section 28h and the mutual inductance between the sections would be of the order of 1/33rd henry, and for resonance therewith to the main ripple frequency of 120 cycles a condenser ofabout 60 microfarads would be indicated. Actually I satisfactorily employed for condenser 33 a capacity of 25 to 30 microfarads, the alternating current through the condenser 33 was of the order of 1.4 amperes, corresponding to any alternating voltagethereacross of the order of volts peak; accordingly I have found it possible to use for condenser 33 an inexpensive electrolytic capacity.

It will be understood that these values are not recited with a limiting intention, nor indeed as examples of the best possible apportionment of parameters for the device in question. They are simply directed to the further specication oi one particular embodiment of my invention, which however is obviously capable of embodiment in a wide variety of discharge devices and systems. Likewise it will be understood that many modifications of the structures herein disclosed may be made without departure from the true spirit and scope of my invention.

In the claims hereto appended I intend to claim not only the entire combination which l have disclosed, but also all its various novel elements and sub-combinations, in emh case as broadly as the state of the art will permit.

I claim:-

1. In combination in a gaseous discharge device, a pair of relatively closely spaced anodes, a thermionic cathode substantially spaced from said anodes and adapted to receive therefrom an arc discharge, means for applying to said anodes opposed alternating potentials, and a second thermionic cathode closely adjacent said anodes and forming therewith a full-wave rectifier.

2. In combination, a gaseous discharge device comprising anode means and a thermionic cathode adapted to receive therefrom an arc discharge, an inductance and an alternating voltage source serially interposed between said anode means and said cathode, and means inductively coupled to said inductance for opposing current fluctuations therein.

3. In combination, a gaseous discharge device and therein a pair of relatively closely spaced anodes and a thermionic cathode substantially spaced from said anodes and adapted to receive therefrom an arc discharge, means for raising the potentials of said anodes alternately above the potential of said cathode, a second thermionic cathode closely adjacent said anodes, and means connected to said second cathode for opposing fluctuations in said discharge.

4. In combination, a gaseous discharge device and therein a pair of relatively closely spaced anodes and a thermionic cathode substantially spaced from said anodes and adapted to receive therefrom an are discharge; means for applying opposed alternating potentials to said anodes; a rectifier comprising anodes respectively connected to said opposed potential applying means, and a cathode; and circuit means connected to said rectifier cathode for opposing uctuations in said discharge.

5. In combination, a gaseous discharge device and therein a pair of anodes and a thermionic cathode adapted to receive therefrom an arc discharge, means for alternately raising the potentials of said anodes, an element adapted to approximate in potential the potential of the instantaneously more positive said anode, and circuit means connected to said element for 'opposing uctuations in said discharge. l

6. In combination, a gaseous discharge device and therein a pair of anodes and a thermionic cathode adapted to receive therefrom an arc discharge, means for alternately raising the potentials of said anodes, choke means between said cathode and said potential raising means, an element adapted to approximate in potential the potential of the instantaneously more positive said anode, and meansy connected to said element and inductively coupled to said choke means, for inducing in said choke means ripple voltages to oppose voltage uctuations between said cathode and the instantaneously more positive said anode.

7. In combinaton, a gaseous discharge device and therein a pair of anodes, and a thermionic cathode adapted to receive therefrom an arc discharge; means for applying opposed alternating potentials to saidl anodes; choke means between said cathode and said potential applying means; a rectifier comprising anodes respectively con-` nected to said opposed potential applying means, and a cathode; and means, connected to said rectier cathode and inductively coupled to said choke means, for inducing in said choke means ripple voltages to oppose current fluctuations therein.

8. In combination, a gaseous discharge device and therein a pair of anodes and a thermionic cathode adapted to receive therefrom an arc discharge; sources of opposed alternating potentials respectively connected to said anodes; a choke coil between said cathode and said sources; a second thermionic cathode closely adjacent said lanodes; and a circuit connected between said second' cathode and said choke coil, comprising serially a condenser and anauxiliary coil tightly coupled to said choke coil.

9. In combination, a gaseous discharge device and therein a pair of anodes and a thermionic cathode adapted to receive therefrom an arc discharge; sources of opposed alternating potentials respectively connected to said anodes; a choke coil betweensaid cathode and said sources; a second thermionic cathode closely adjacent said anodes; a circuit connected between said second cathode and said choke coil, comprising serially a condenser and an auxiliary coil tightly coupled to said choke coil; and a second choke coil, interposed between said irst choke coil and said sources. of a value substantially greater than required for resonance with` said auxiliary coil and said condenser to twice the frequency of said alternating potentials.

10. A discharge system comprising, in combination, a gaseous discharge device and therein a pair of anodes and a thermionic cathode adapted to receive therefrom an arc discharge; sources of opposed alternating potentials respectively connected to said anodes; a choke coil between said cathode and said sources; a second thermionic cathode closely adjacent said anodes; a circuit for inducing in said choke coil a ripple voltage whereby to oppose ripple currents therein, comprising an auxiliary coil tightly coupled to said choke coil 4and a condenser, and serially connected between said second cathode and said choke coil; and means for retarding the phase of ripple currents in the system, whereby to bring the ripple current through said circuit more nearly into phase with said anode potentials.

11. In combination, a gaseous discharge device and therein anode means and a thermionic cathode substantially spaced from said anode means and adapted to receive therefrom an arc discharge; an alternating voltage source connected to said anode means; a choke coil between said source and said cathode; a second thermionic cathode closely adjacent said anode means and forming therewith a rectifier; and means for producing an inductive kick across said choke coil, comprising a conductive circuit serially including circuit-breaking means responsive to a predetermined circuit current, said circuit being adapted to conduct current from said source through said rectifier and said choke coil, and being connected between said two cathodes.

12. In combination, a gaseous discharge device and therein a filling 'of gas, anode means, and a thermionic cathode substantially spaced from said anode means and adapted to receive therefrom an arc discharge; an alternating voltage source between said anode means and said cathode; a second thermionic cathode closely adjacent said anode means; means, operative at a time interval after said source is rendered operative, for ionizing said gas whereby to start said luminous discharge;,and a condenser, connected between said second cathode and a point intermediate said source and said first cathode, whereby to maintain said second cathode at a high positive potential at the instant of said gas ionization.

13. In combination, a gaseous discharge device and therein anode means and a thermionic cathode substantially spaced from said anode means and adapted to receive therefrom an aro discharge; an alternating voltage source connected val aftersaidsource is rendered operative; means responsive to said increased current for breaking said circuit, whereby to produce across said choke coil an inductive kick; and a condenser connected from said second cathode to said choke coil, whereby to render said current substantially smooth and to maintain said second cathode at a high positive potential at the instant of said kick. 14. In combination, a gaseous discharge device and therein a filling of gas, a pair of anodes, and a thermionic cathode substantially spaced from said anodes and adapted to receive therefrom an arc discharge; sources of opposedv alternating potentials respectively connected to said anodes; a choke, coil between said cathode and said sources; an auxiliary coil tightly coupled to said choke' coil and connected thereto; a second cathode closely adjacent said anodes; means, operative at'a time interval after said sources are rendered operative, for ionizing said gas whereby to start said-luminous discharge; Vand a condenser, connected between said second cathode and said auxiliary coil, whereby to maintain said second cathode at a high positive potential at the instant of said gas ionization and thereafter to oppose current fluctuations in said choke coil.

15. The combination according to claim 1, further including a shield can surrounding said second cathode, provided with discharge-conducting apertures, and electrically connected to said sec- 4ond cathode.

16. In a gaseous discharge device, a rectifying structure comprising a therniionic cathode; a cylindrical shield can surrounding said cathode and provided on respectively opposite sides with two discharge conducting apertures; and a pair of anodes adjacent said can on opposite sides thereof, in a planeaxial of said can and at right angles to the axial plane containing said apertures. s

17. In a gaseous discharge device, a rectifying structure comprising a thermionic cathode; a cylindrical shield can surrounding said cathode and provided on respectively opposite sides with two discharge conducting apertures; a pair of anodes adjacent said can on opposite sides thereof, in a plane axial of said can and at iight angles to the axial plane containing said apertures; and anode shielding vanes extending from said can in substantially a single axial plane, each vane being closely spaced from a respective said anode.

18. In a gaseous discharge device, anode means and an electron-emissive cathode adapted to receive therefrom an arc discharge, said cathode being of hollow formation and being both internally and externally emissive; and means for forcing substantially the entire said discharge into the space bounded by interior surface of said cathode, comprising apertured shielding means in close spaced relationship to the exterior surface of said cathode.

i9. In a gaseous discharge device, anode means and an eleetron-emissve. cathodeadapted to receive therefrom an arc discharge, said cathode being an open-walled hollow body; tured shielding means in sumciently close spaced relationship to the outside oi said body to force substantially the entire said discharge into the space within said body. y

20. in agaseousA discharge device, anode means and an electron-emissivecathode adapted to receive therefrom an arc dischargasaid cathode comprising a thermionic helix wound in two spaced sections; and shielding means surrounding and close to said helix and provided with discharge-conducting sections and adapted to guide the discharge internally of said helix, the internal radius of said.

helix' being several times greater than the mean and aperstarting of said apertures intermediate saidfree path length of the electrons emitted by said cathode during said discharge.

21. In a gaseous discharge device, anode means and an electron-emissive cathode adapted to receive therefrom an arc discharge, said cathode comprising a. heater wire in the form oi a helix wound in several sections .spaced apart, a ne wire wound about and in intimate contact with said heater wire, and an oxide coating over said wound heater wire; means for'passing a heating current through said heater wire; and shielding means surrounding and close to said helix and provided with discharge-conducting apertures adapted to guide the discharge intermediate of said sections and internally of said helix.

22. In a gaseous discharge device, anode means and an electron-emissive cathode adapted to receive therefrom anarc discharge, said cathode comprising a therinionic helix; and shielding means surrounding and'close to said helix and provided with discharge-conducting apertures in termediate the extremities of said helix; said apertures beingl sumciently small to produce an appreciable potential gradient in the discharge passing therethrough, said helix being provided with a longitudinal spacing adjacent to and oi substantially greater length than said apertmes,

and the radius of said helix being several times greater than the mean free path length of the electrons emitted by said cathode during said discharge.

23. In a gaseous discharge device, anode means and an electron-emissive cathode adapted to receive therefrom an` arc discharge, said cathode comprising a thermionic helix; surrounding and close to said helix and provided with relatively small discharge-conducting apertures adapted to guide the discharge internally of said helix; a constant-current transformer having a, heating secondary connected across said helix and having a discharge-supporting secondary connected between said cathode and said anode means; and means ior delaying the discharge for a time interval after said transformer is energized. s l

24. In a gaseous discharge device, anode means and an electron-emissive cathode adapted to receive therefrom an arc discharge, said cathode comprising a pair of axially aligned hollow bodies; and shielding means in close spaced relationship tothe outside of said bodies, said means being apertured between said bodies for the admission of said discharge to their interiors.

CARL J. R. H. von WEDE...

shielding means 

